Methods of manufacturing fluid-dynamic-pressure bearing and spindle motor incorporating the bearing, and spindle motor and recording-disk drive incorporating the bearing

ABSTRACT

In spindle motors journaled on fluid-dynamic-pressure bearings, especially in such spindle motors employed in recording-disk drives in implementations that subject the drives to vibration and shock, sealing performance of a capillary seal formed between motor rotor-side and stator-side bearing surfaces, cohesiveness of oil-repellant on rotor-side/stator-side dry-area surfaces adjoining the capillary seal section, and motor inter-component adhesive strength are improved. The capillary-seal-constituting rotor-side/stator-side surface(s) are exposed to a plasma or to ultraviolet rays under predetermined conditions to improve the wettability of the surface(s) for the bearing fluid. The dry-area surface(s) are similarly irradiated so as to improve their wettability for the oil-repellant. Adhesively bonded component surfaces are likewise irradiated so as to improve their wettability for the adhesive, enhancing adhesive strength. Exposed surfaces may be constituted of a synthetic resin to enhance their wettability further, or may be made of metal, to yield a cleaning efficacy from the plasma/UV exposure.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Divisional of U.S. non-provisional patent application Ser. No.10/908,191, filed on May 2, 2005 and issued as U.S. Pat. No. 7,650,697on Jan. 26, 2010, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to fluid-dynamic-pressure bearingmanufacturing methods, to spindle motor manufacturing methods, and tospindle motors and recording-disk drives.

2. Description of the Related Art

In recent years, the amount of information that is recorded per unitarea on discoid recording media in hard-disk and like recording-diskdrives has been increasing, and the information density has been on therise. The increasing recording density has led to calls for stablysupporting the discoid recording media under high-speed rotation.

Recording-disk drives, meanwhile, are finding applications other than instationary computers, such as desk-top and server machines, in which thedrives have been traditionally employed, and are being used in vehiculardevices, portable devices, and other mobile devices. Such mobileapplications have led to rising demands for impact resistance andlongevity-demands without precedent in implementations in which thedrives are employed under environments, as has conventionally been thecase, that do not subject the drives to vibration and shock.

Against this backdrop, the development of bearings for stably supportingdisk-drive rotor units under high-speed rotation has been ongoing.

In order that the bearings meet this demand, considerations of paramountimportance are:

(A) Improvement in the sealing performance of the bearing's capillaryseal section;

(B) Improvement in the ability to prevent wetting diffusion along thesurfaces in the vicinity of the capillary seal; and

(C) Improvement in the joint strength of the components that constitutethe dynamic-pressure bearing and the spindle motor.

Consideration (A)

Fluid-dynamic-pressure bearings are composed of a journal unit and ajournal-support unit, between which is formed a narrowed micro-gap. Alubricating fluid such as oil is retained within the gap. An oil sealingmechanism referred to as a capillary seal section is provided in thepart of the bearing in which the micro-gap is open to the externalatmosphere. The capillary seal section is of a form in which the gapbetween the journal and, opposing the journal, seal surfaces on thebearing's journal-support side gradually flares going axially upward. Aboundary surface between the oil and the external atmosphere forms inthe capillary seal section.

If the lubricating fluid is not sealed in by the capillary seal section,the fluid ends up leaking out to the exterior. As a consequence, thelubricating fluid retained in the micro-gap runs short, ultimatelycurtailing the lifespan of the bearing. In bearing implementations inminiature spindle motors in particular, since the gross amount of oilretained inside the bearing is very little, if even a slight amount ofthe lubricating fluid manages to leak out, an oil shortfall is liable tooccur. Furthermore, the problem of weak sealing performance in capillaryseals can allow shock or other impact on the bearing to disturb theintegrity of the seal boundary surface.

Keeping the angle of contact between the oil and the components thatconstitute the capillary seal section small is crucial to enhancing thestrength of capillary seals.

Consideration (B)

Oil repellant is applied to the surfaces of the components thatconstitute the outer side of the capillary seal section. Applying oilrepellant prevents lubricating fluid from the capillary seal sectionfrom migrating along the bearing component surfaces to the bearingexterior by wetting-diffusion.

The way oil repellants are applied is to spread repellant that has beendissolved in a solvent onto the component surfaces, and vaporize thesolvent to get the oil repellant to adhere to the surfaces.

Nevertheless, the wettability of the oil repellant for the sealcomponent surfaces is poor, which has meant that therepellant-to-surface adhesiveness has not been satisfactory.Consequently, oil mop-up or associated concluding operations inmanufacturing dynamic-pressure bearings cause the oil repellant to peeloff easily. Although processes such as striating the components orspreading the oil repellant on thickly have been implemented to date onaccount of the behavior of the repellant, such processes elevate thecomponent cost, and, moreover, have not amounted to a fundamentalsolution.

Consideration (C)

Spindle motors for hard-disk drives are furnished with a base componentand, anchored to the base component, a cylindrical sleeve housing thatserves as a stator-side bearing component. The outer circumferentialsurface of the sleeve housing is, by an interposed adhesive, fixed tothe inner circumferential surface of a mounting hole formed in the basecomponent.

The slightest warpage or deformation in spindle-motor bearing componentsbecomes a problem particularly in fluid-dynamic-pressure bearings, inthat the bearing gaps are extraordinarily narrow. On that account, inthe plurality of inter-component junctions, adhesive anchoring by meansof an adhesive agent is often employed instead of welding, in whichthermal deformation is liable to occur.

Especially under environments, such as in mobile and vehicular devices,that place vibration and shock on the bearings, particularly large loadsare placed on the joints between components. More particularly, theability to withstand serious shock—in excess of 1000 Gs—can be mandatoryin situations in which there is a likelihood of the devices beingdropped. Consequent on the scaling down of spindle motors, however, isan abridgement of the inter-component binding length, which has madeimproving the binding strength a challenge.

BRIEF SUMMARY OF THE INVENTION

A first object of the present invention is to make available amanufacturing method that enables the adhesive strength in spindlemotors to be improved.

A second object of the present invention is to afford a method ofmanufacturing fluid-dynamic-pressure bearings that enables the sealingperformance of the capillary seal section to be improved.

A third object of the present invention is to make available a method ofmanufacturing fluid-dynamic-pressure bearings that enables oil repellantfor oil-repelling surfaces to be cohered stably to the oil-repellingsurfaces.

A fluid-dynamic-pressure bearing to which a fluid-dynamic-pressurebearing manufacturing method that is a first aspect of the presentinvention is applicable has the following configuration. Namely, thefluid-dynamic-pressure bearing comprises a stator unit and a rotor unitthat is rotary with respect to the stator unit. The stator unit and therotor unit oppose each other across a micro-gap. A lubricating fluidfills and is retained within the micro-gap.

A clearance that communicates with the micro-gap is formed in betweenthe stator unit and the rotor unit. The portion of the clearance thatcommunicates with the micro-gap serves as the capillary seal section. Aboundary surface between the lubricating fluid and the externalatmosphere forms in the capillary seal section. Surfaces of the statorunit and rotor unit oppose to form the capillary seal section.

The first aspect of the present invention, being afluid-dynamic-pressure bearing manufacturing method as just set forth,includes at least the following first and second steps. In the firststep, a surface-treating process consisting of at least one betweenplasma irradiation and ultraviolet-beam irradiation is implemented on atleast one between a rotor-side surface and a stator-side surface thatconstitute the capillary seal section. In addition, after (which neednot be directly after) the first step has been effected, the secondstep, in which lubricating fluid is infused into the micro-gap, iseffected.

The first step in the first aspect of the invention may be effectedbefore the rotor unit and the stator unit of the fluid dynamic-pressurebearing are assembled. In particular, the respective parts of the rotorunit and the stator unit may individually undergo the surface-treatingprocess of the first step. Likewise, the surface-treating process of thefirst step may be effected on both the stator unit and the rotor unit,which may be on the rotor unit and stator unit simultaneously, or not atthe same time.

Bearing manufacturing procedures including assembling, heating,pressurizing, and cleaning may be effected in between the first step andthe second step.

Embodying the first aspect of the invention improves the wettability,with respect to organic substances, of the surfaces that constitute thecapillary seal section, rendering the wetting angle extremely small. Theimproved wettability consequently improves the sealing performance ofthe capillary seal. An added advantage is that ultraviolet-beam andplasma irradiation of the capillary seal section surfaces(s) decomposeand clean off metal-surface clinging organic matter, which is given todeteriorating the quality of the lubricating fluid. A still furtherbenefit is that ultraviolet-beam and plasma irradiation do not requirethe use of chemicals that are hazardous to the environment. What ismore, compared with processing surfaces using chemicals or by machiningthe relevant parts, the work in carrying out ultraviolet-beam and plasmairradiation is simple and the operation time is short. Operability andproductivity therefore improve.

Furthermore, the second-step process of charging the bearing gap withlubricating fluid is the more advantageously effected through thecapillary seal section. Charging the bearing via the surface(s) whosewettability has been improved by undergoing ultraviolet-beam or plasmairradiation keeps the lubricating fluid from incorporating air bubbles.The lubricating fluid infusion volume can therefore be adjusted moreaccurately.

Further to the first aspect of the present invention, advantageously atleast one among the stator-unit and rotor-unit surfaces that constitutethe capillary seal section is formed of a resin material. Resins areactivated superficially by plasma irradiation or ultraviolet-beamirradiation, and thus constituting the seal-section surface(s) from aresin material improves the wettability of the surface(s) forlubricating fluid.

Still further to the first aspect of the invention, at least one amongthe stator-unit and rotor-unit surfaces that constitute the capillaryseal section may be formed of metal. In the manufacturing method in thatcase, advantageously the surface-treating process, by means of at leastone between plasma irradiation and ultraviolet-beam irradiation, in thefirst step is carried out over a broader extent on the metal components.Plasma-based cleaning or cleaning using ultraviolet beams dissolvesgrease and other grime clinging to the metal surfaces, and therefore areideally suited to the cleaning of bearing components, in which a highlevel of cleanliness is mandatory. Effecting cleaning by means of thefirst step enables the cleaning process and the surface-treating processto be carried out at the same time, which makes for excellentoperability of the manufacturing method.

Yet further to the first aspect of the present invention, at least onesurface-treating process among the group of surface-treating processesconsisting of plasma irradiation and ultraviolet-beam irradiation isimplemented on at least any one surface among the stator-unit androtor-unit surfaces that constitute the micro-gap.

The surfaces of the micro-gap constitute the bearing faces of the fluiddynamic-pressure bearing. Improving the wettability of the surfaces forthe lubricating fluid enhances the bearing's ability to retainlubricating fluid between the stator-unit surfaces and the rotor-unitsurfaces. The heightened inter-surface lubricant retaining abilitycontributes to preventing the stator-unit surfaces and rotor-unitsurfaces from contacting, even as the bearing withstands stronger shocksand vibrations.

A fluid-dynamic-pressure bearing to which a fluid-dynamic-pressurebearing manufacturing method that is a second aspect of the presentinvention is applicable has the following configuration. Namely, thefluid-dynamic-pressure bearing, in a like manner as thefluid-dynamic-pressure bearing in the first aspect of the invention,comprises a stator unit and a rotor unit that is rotary with respect tothe stator unit. Further, a capillary seal section is formed in the samemanner as in the first aspect of the invention. A boundary surfacebetween the lubricating fluid and the external atmosphere forms in thecapillary seal section.

In addition, a dry-area face adjoining the capillary seal section isprovided on at least one of either of the stator unit or rotor unit. Thedry-area face is formed in order for the surface to be coated with oilrepellant.

The second aspect of the present invention, being afluid-dynamic-pressure bearing manufacturing method as just set forth,includes the following first, second and third steps. In the first step,a surface-treating process consisting of at least one between plasmairradiation and ultraviolet-beam irradiation is implemented on thedry-area face on at least one of either of the stator side or rotor sideof the bearing. Furthermore, after (which need not be directly after)the first step, the second step, in which oil repellant is applied tothe dry-area face(s), is effected. In addition, after (which need not bedirectly after) the second step, the third step, in which the inside ofthe micro-gap is charged with lubricating fluid, is effected.

As is the case with the first step in the first aspect of the presentinvention, it does not matter whether the first step in the secondaspect of the invention precedes or follows the bearing assemblyprocess. Furthermore, in implementations in which the first step iseffected on both the stator unit and the rotor unit, it may be sosimultaneously, or not at the same time. Additionally, other proceduresassociated with manufacturing the bearing, including assembling,heating, pressurizing, and cleaning may as needed be effected in betweenthe first step and the second step, or between the second step and thethird step.

Embodying the second aspect of the invention improves the wettability,in the dry-area face(s), between the dry-area face(s) and the oilrepellant. This improved wettability prevents the oil repellant fromexfoliating (peeling off). Accordingly, lubricating fluid is preventedfrom migrating by wetting-diffusion over the dry-area face(s) continuouswith the capillary seal.

Since in particular the dry-area face of the rotor unit is susceptibleto wetting diffusion due to centrifugal force when the rotor unit spins,the fourth step is advantageously effected on the dry-area face of therotor unit so that the oil repellant does not peel off.

In the second aspect of the present invention, further advantageously asurface-treating process consisting of at least one between plasmairradiation and ultraviolet irradiation is implemented on one of eitherof the stator unit and rotor unit where the capillary seal section isformed.

Moreover, inasmuch as the face(s) constituting the dry-area face(s), andthe surfaces constituting the capillary seal section adjoin each other,treating the surfaces at the same time makes for efficient manufacturingwork.

The foregoing surface-treating processes improve the lubricating-fluidretaining ability of the capillary seal section and prevent the oilrepellant from peeling off, which all the more effectively prevents thelubricating fluid from leaking out.

Further to the second aspect of the present invention, advantageously atleast one among the stator-unit and rotor-unit surfaces that constitutethe capillary seal section is formed of a resin material. Resins arereadily activated at the surface by plasma irradiation orultraviolet-beam irradiation, and thus constituting the seal-sectionsurface(s) from a resin material improves the cohesion between thesurface(s) and the oil repellant.

Still further to the second aspect of the invention, the dry-area faceon at least one of either of the stator-unit side and the rotor-unitside of the bearing may be formed of metal. In the manufacturing methodin that case, advantageously the surface-treating process, by means ofat least one between plasma irradiation and ultraviolet-beamirradiation, is carried out over a broader extent on the metalcomponents. Plasma-based cleaning or cleaning using ultraviolet beamsdissolves grease and other grime clinging to the metal surfaces, andtherefore are ideally suited to the cleaning of bearing components, inwhich a high level of cleanliness is mandatory. Also, the cleaningprocess and the surface-treating process may be carried out at the sametime, which makes for excellent operability of the manufacturing method.

Yet further to the second aspect of the present invention, at least onesurface-treating process among the group of surface-treating processesconsisting of plasma irradiation and ultraviolet-beam irradiation isimplemented on at least any one surface among the stator-unit androtor-unit surfaces that constitute the micro-gap.

The surfaces of the micro-gap constitute the bearing faces of the fluiddynamic-pressure bearing. Improving the wettability of the surfaces forthe lubricating fluid enhances the bearing's ability to retainlubricating fluid between the stator-unit surfaces and the rotor-unitsurfaces. The heightened inter-surface lubricant retaining abilitycontributes to preventing the stator-unit surfaces and rotor-unitsurfaces from contacting, even as the bearing withstands stronger shocksand vibrations.

A spindle motor to which a spindle-motor manufacturing method that is asecond aspect of the present invention is applicable has the followingconfiguration. Namely, the spindle motor is furnished with a basecomponent, a stator unit fixed to the base component, and a rotor unitsupported to let it rotate with respect to the stator unit. The basecomponent is the baseplate of the spindle motor. In implementations inwhich the spindle motor is a DC brushless motor, a stator around whichcoils are wound is anchored to the base component or to the stator unit.

The stator unit defines an outer circumferential surface. The basecomponent is furnished with an adhesion surface of conformationcorresponding to the form of the stator-unit outer circumferentialsurface. The stator unit is adhesively affixed to the base component.

The third aspect of the present invention, being a spindle-motormanufacturing method as just set forth, includes the following firstthrough third steps. Namely, in the first step, at least onesurface-treating process among the group of surface-treating processesconsisting of plasma irradiation and ultraviolet-beam irradiation isimplemented on at least one of either of the outer circumferentialsurface of the stator unit or the adhesion surface of the basecomponent. In the second step, which is effected following the firststep, an adhesive agent is applied to at least one of either of theouter circumferential surface of the stator unit or the adhesion surfaceof the base component.

Subsequently, in the third step, the stator unit is inset into the basecomponent, with the stator-unit outer circumferential surface fitting tothe base-component adhesion surface, whereby the stator unit and thebase component cohere via the adhesive agent. Furthermore in the thirdstep, the adhesive agent is hardened to fix the stator unit to the basecomponent. Examples of how the adhesive agent would be hardened include:by heating it, if the adhesive is thermosetting; by shielding it fromthe air, if the adhesive is anaerobic; by irradiating it with anultraviolet beam if the adhesive is UV curing; and by mixing it with ahardener if the adhesive involves a two-component system.

Embodying the third aspect of the invention improves the wettability,with respect to organic substances, of the surfaces adhered by theadhesive agent, which therefore improves the cohesiveness between theadhesive agent and the adhering surfaces. In this way the adhesivestrength when the adhesive is set improves. Moreover, the fact that thewettability of the surfaces for the adhesive agent is improved enablesthe adhesive to enter into the narrow gap between the stator unit andthe base component to yield more powerful adhesive strength. The spindlemotor is therefore made tougher, especially against disturbances such asshock and vibration, which makes for longer motor lifespan.

Further to the third aspect of the present invention, advantageously atleast one between the outer circumferential surface of the stator unitand the adhesion surface of the baseplate is formed of a resin material.Resins are readily activated at the surface by plasma irradiation orultraviolet-beam irradiation, and thus constituting thestator-unit/baseplate surface(s) from a resin material improves thewettability between the surface(s) and the adhesive agent.

Further yet to the third aspect of the invention, at least one of eitherof the outer circumferential surface of the stator unit and the adhesionsurface of the baseplate may be formed of metal. In the manufacturingmethod in that case, advantageously the surface-treating process, bymeans of at least one between plasma irradiation and ultraviolet-beamirradiation, is carried out over a broader extent on the stator unit andthe baseplate. Plasma-based cleaning or cleaning using ultraviolet beamsdissolves grease and other grime clinging to the metal surfaces, andtherefore are ideally suited to the cleaning of spindle motors, in whicha high level of cleanliness is mandatory. Also, the cleaning process andthe surface-treating process may be carried out at the same time, whichmakes for excellent operability of the manufacturing method.

The performance of the capillary seal section in a spindle motorutilizing a fluid-dynamic-pressure bearing manufactured by amanufacturing method of the first aspect of the present invention issuperior, and this heightened capillary-seal performance contributes toproducing spindle motors that are of extended lifespan and are toughagainst impact.

In turn, a spindle motor utilizing a fluid-dynamic-pressure bearingmanufactured by a manufacturing method of the second aspect of theinvention enables the surfaces onto which the oil repellant is appliedto maintain stabilized oil repellency, which, by preventing wettingdiffusion of the lubricating fluid, contributes to producing spindlemotors of prolonged lifespan.

A recording-disk drive utilizing a spindle motor manufactured by amanufacturing method of the third aspect of the present inventionespecially improves the motor's longevity and resistance to impact. Inimplementations in which the base component constitutes part of thedisk-drive case, exit/entry of air internal/external to therecording-disk drive can be prevented, which keep contaminants fromentering into the interior of the case.

From the following detailed description in conjunction with theaccompanying drawings, the foregoing and other objects, features,aspects and advantages of the present invention will become readilyapparent to those skilled in the art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of a recording-disk drive of the presentinvention;

FIG. 2 is a sectional view of a fluid-dynamic-pressure bearing, and aspindle motor in which the bearing is utilized, involving a firstembodiment of the present invention;

FIG. 3 is a sectional view of a fluid-dynamic-pressure bearing, and aspindle motor in which the bearing is utilized, involving a secondembodiment of the present invention;

FIG. 4 is a sectional view of a fluid-dynamic-pressure bearing, and aspindle motor in which the bearing is utilized, involving a thirdembodiment of the present invention; and

FIG. 5 is an enlarged fragmentary sectional view, in which a blowup ofthe capillary seal section is inset, illustrating key features of afluid-dynamic-pressure bearing of the present invention.

FIG. 6 is a flowchart showing a preferred embodiment of a method used tomanufacture a spindle motor in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An explanation of modes of embodying the present invention will be madewhile referring to the drawings. It should be understood that in thedescription of the embodiments, when terms that indicate directions areused without special notation, the terms indicate directions representedin the drawings; consequently such noting does not limit orientations inembodying the invention.

First Embodiment

In the present embodiment, a fluid-dynamic-pressure bearing for which amanufacturing method of the present invention is utilized is employed ina spindle motor 3 that spins discoid recording media.

Hard-Disk Drive

Reference is made to FIG. 1, which is a sectional view illustrating ahard-disk drive 1 that is a recording-disk drive device embodying thepresent invention. The hard-disk drive 1 is in the interior of a case 11furnished with a spindle motor 3 that spins recording disks 12, heads 13that read information from and write information into the recordingdisks 12, and an actuator unit 14 that shifts the heads 13 into selectlocations over the recording disks 12.

Spindle Motor Configurational Outline

The spindle motor 3 is, as depicted in FIG. 2, furnished with: a rotorhub 21 having a carrying surface on which the recording disks 12 arecarried; a toroidal rotor magnet 32 attached to the rotor hub 21; abracket 27 that serves as the base component; a stator 31 made up of aplurality of coils; and a fluid-dynamic-pressure bearing 2 thatrotatively supports the rotor hub 21 and rotor magnet 32 with respect tothe bracket 27 and stator 31. The stator 31 is fixed to the bracket 27,radially opposing the inner circumferential surface of the rotor magnet32. The fluid-dynamic-pressure bearing 2 is mounted in, unitized with,the bracket 21. It should be noted that the bracket 27 may be integratedwith the case 11 to constitute the baseplate (base component).

Fluid-Dynamic-Pressure Bearing Configuration

The fluid-dynamic-pressure bearing 2 is furnished with: a shaft 24 fixedinto the rotor hub 21; a sleeve 22 fit over the shaft 24; asubstantially cup-shaped bearing housing 23 on the radially outer sideof the sleeve 22, and into which the sleeve 22 is inset; and a sealbushing 26 mounted in a location to the upper side of the sleeve 22. Therotor hub 21 and the shaft 24 constitute the rotor unit; the bearinghousing 23, the sleeve 22, and the seal bushing 26 constitute the statorunit.

The shaft 24 defines a cylindrical outer circumferential surface. Thesleeve 22 is formed of a sintered porous metal, and the sleeve 22defines a cylindrical inner circumferential surface that radiallyopposes the outer circumferential surface of the shaft 24. The outercircumferential surface of the sleeve 22 is adhesively affixed to theinner circumferential surface of the bearing housing 23. The bearinghousing 23 is formed of a resin such as a liquid-crystalline polymer.

Radially extending and axially extending gaps between the shaft 24 andthe sleeve 22 are charged with and retain a lubricating fluid 35. Anester-based or a poly(.alpha.-olefin) based oil is, for example,utilized as the lubricating fluid 35. It will be appreciated that forthe lubricating fluid 35, oils or other liquids appropriately selectedand adjusted according to the how the lubricating fluid is to performmay be utilized.

At least a portion of the outer circumferential surface of the shaft 24and of the inner circumferential surface of the sleeve 22 are radiallyspaced apart by several μm, wherein a radial dynamic-pressure bearing 42is formed. The shaft 24 is flanged adjacent the end on its lower side,forming a radially outward extending flange 25, and the upper and lowersurfaces of the flange 25 axially oppose the bottom surface of thebearing housing 23 and the lower endface of the sleeve 22, whereinrespective thrust dynamic-pressure bearings 43 a and 43 b areconstituted.

The radial dynamic-pressure bearing 42 and the thrust dynamic-pressurebearings 43 rotatively support the shaft 24 and the rotor hub 21 withrespect to the sleeve 22, by the force of pressure produced due to thedifference in flow speed of the lubricating fluid 35 retained in thegaps in between the rotating shaft 24 and the sleeve 22 opposing theshaft. Further, dynamic-pressure grooves (not illustrated) ofherringbone conformation, that when the shaft 24 rotates with respect tothe sleeve 22 exert a pumping action on the lubricating fluid 35 in adirection gathering the fluid into an axial stretch of the radialdynamic-pressure bearing 42, are formed on the radial-bearingconstituting, inner-circumferential surface of the sleeve 22.

The description now turns to FIG. 5, which is a fragmentary viewenlarged from FIG. 2 to show key features of the seal bushing 26 and theshaft 24. The interval between the outer circumferential surface of theshaft 24 and the inner circumferential surface of the seal bushing 26flares as the spacing heads upward. Herein the bearing 2 is configuredso that at the lower end of the seal bushing 26 the spacing is about 20μm, and at the upper end of the seal bushing 26 it is about 300 μm. Inthe spacing, a boundary surface 44 between the lubricating fluid 35 andthe external atmosphere forms, constituting a capillary seal. Theposition of the boundary surface 44 is determined by the measure ofsurface tension acting on the interface between the lubricating fluid 35and the external atmosphere; the stronger this surface tension is, themore stably the boundary surface 44 is maintained. The size of thespacing for the capillary seal, and the size θ1 of the wetting anglebetween the lubricating fluid 35 and the surfaces that constitute acapillary seal section 41 greatly influence the strength of the surfacetension.

Manufacturing Method

A preferred embodiment of a method of manufacturing a spindle motor isdescribed below with reference to FIG. 6.

Processing & Cleaning

Namely, to begin with the rotor hub 21, the sleeve 22, the bearinghousing 23, the shaft 24, the seal bushing 26, and the base component 27are respectively machined/formed. Thereafter the components are cleaned.Purified water, solvents, acidic/alkaline solutions, surface-activeagents, etc. are utilized for the cleaning.

Herein, cleaning by means of ultraviolet-beam irradiation or plasma,such as UV-ozone cleaning, may be carried out. Cleaning employing UVrays or plasma makes it possible to achieve highly effective cleansingon grime due to organic residues. What is more, both the liquid-basedand irradiation-based cleaning processes may be carried out jointly.

UV-Beam Irradiation of Sleeve Outer Circumferential Surface

Next, the outer circumferential surface of the sleeve 22 is irradiatedwith an ultraviolet beam. The UV beam has a distinct spectrum that, forexample, with a mercury lamp is 365 nm, and in an implementation inwhich a low-pressure mercury lamp is utilized, is 185 nm, 254 nm; and inan implementation in which an excimer lamp is utilized, the spectrum is126 nm, 146 nm, 172 nm, 222 nm. In order to have the irradiation be UVrays in a specific bandwidth alone, the light can be put throughfiltering and beam-splitting as required to render single-wavelengthcomponents exclusively. The exposure duration is about 20 seconds.

Subsequently the outer circumferential surface of the bearing housing 23is irradiated with an ultraviolet beam. The UV irradiation is equivalentto that effected on the outer circumferential surface of the sleeve 22.The exposure duration is about 20 seconds.

UV-Beam Irradiation of Seal Bushing

Next, the upper endface and the inner circumferential surface of theseal bushing 26 are irradiated with an ultraviolet beam. The UV beam isthe same as that with which the outer circumferential surface of thesleeve 22 is irradiated, and is output from the same light source. Theexposure duration is about 20 seconds, and the cumulative dose is set tobe 35 kJ/m². The upper endface of the seal bushing 26 serves as astator-side oil-repellant application surface 46 a, while the innercircumferential surface of the seal bushing 26 serves as a stator-side,capillary seal section 41 constituting seal surface 45 b.

It will be appreciated that these UV exposure operations enablesurface-cleansing effectiveness to be achieved. Cleaning employingultraviolet rays or plasma makes it possible to achieve highly effectivecleansing on grime due organic residues.

Assembly

Next, the shaft 24 is inserted into the sleeve 22, and the sleeve-shaftassembly is inset into the bearing housing 23. The sleeve 22outer-circumferential surface and the bearing housing 23inner-circumferential surface are adhesively affixed to each other.Insetting the sleeve 22 by press-fitting it into the bearing housing 23runs the risk that warpage in the sleeve 22 will occur, but adhesiveaffixation enables the sleeve 22 to be bound to the bearing housing 23without distorting the sleeve 22. Furthermore, since the outercircumferential surface of the sleeve 22 prior to assembly has beenirradiated with ultraviolet rays, the adhesive 34 coheres readily to thesleeve surface, dramatically improving the adhesive strength between thesleeve 22 and the bearing housing 23.

Subsequently, the seal bushing 26 is inset into the bearing housing 23and adhesively affixed to the housing inner-circumferential surface. Theportion of the shaft 24 that opposes the inner circumferential surfaceof the seal bushing 26 serves as a rotor-side, capillary seal section 41constituting seal surface 45 a.

Applying Repellant 33

In the next stage in the bearing 2 manufacturing process, an oilrepellant 33 is applied to a rotor-side oil-repellant applicationsurface 46 b located to the upper side of the seal surface 45 b of theshaft 24. The oil repellant 33 is applied with a special dispenser forthat purpose. A groove that serves to mark the location where therepellant 33 is applied is formed in the oil-repellant applicationsurface 46 b of the shaft.

Infusing Lubricating Fluid 35

Next, through the gap between the seal bushing 26 and the shaft 24,lubricating fluid 35 is infused into the gap between the radialdynamic-pressure bearing 42 and the thrust dynamic-pressure bearings 43.While the assembly is under a vacuum, the lubricating fluid 35 is pouredin so as to conceal the gap between the seal bushing 26 and the shaft24; the assembly is then gradually returned to near atmosphericpressure, whereby the lubricating fluid 35 enters into and is retainedwithin the gaps that constitute the radial and thrust dynamic-pressurebearings. The lubricating fluid 35 is infused in an amount by which theinterior of the gaps will be filled with the lubricating fluid 35.

Subsequently, whether the lubricating fluid 35 is the appropriate amountis examined by gauging the height of the boundary surface 44 between thelubricating fluid 35 and the external atmosphere. When the lubricatingfluid 35 is the proper quantity, the locus of the boundary surface 44will form in between the stator-side seal surface 45 a and therotor-side seal surface 45 b.

By the foregoing method, a fluid dynamic-pressure bearing 2 made up ofthe sleeve 22, the bearing housing 23, the shaft 24, the seal bushing26, and the lubricating fluid 35 retained in the radial fluiddynamic-pressure bearing 45 and the thrust fluid dynamic-pressurebearings 43 is completed.

Mounting Rotor Hub

The rotor hub 21 onto which the rotor magnet 32 has been attached ismounted onto the shaft 24 by press-fitting the hub onto the shaft upperend. As a means to improve the binding strength, as well as in order toprevent deformation of the components, the hub may be fixed to the shaftusing an adhesive.

Anchoring Bearing Unit to Base

Next, the bearing housing 23 is adhesively affixed to the bracket 27onto which the stator 31 has been mounted. A mounting hole 27 a ofsubstantially the same conformation as the outer circumferential surfaceof the bearing housing 23 is formed in the bracket 27. With the adhesive34 intervening, the outer circumferential surface of the bearing housing23 is snugged along the inner circumferential surface constituting themounting hole 27 a, to which the housing circumferential surface isthereby adhesively affixed. Since the outer circumferential surface ofthe bearing housing 23 has been irradiated with ultraviolet rays priorto fixing the housing into the bracket, the adhesive 34 coheres readilyto the housing surface, dramatically improving the adhesive strengthbetween the outer circumferential surface of the bearing housing 23 andthe mounting hole 27 a in the bracket 27.

A spindle motor 3 is manufactured through these steps.

Embodiment Effects/Results

The change in wetting angle in the capillary seal section 41 of afluid-dynamic-pressure bearing 2 in the first embodiment, manufacturedaccording to a manufacturing method of the present invention, will begiven in the following. When an ester-based oil was employed as thelubricating fluid 35, its wetting angle with the seal bushing 26 priorto being exposed to ultraviolet rays was about 60.degree. The wettingangle after a 20-second exposure with a UV beam having a principalwavelength of 185 nm became 20-30.degree. Quite clearly, then, thewetting angle was extraordinarily reduced. Moreover, even after sevendays post UV-exposure the wetting angle remained essentially unchanged.

Prior to implementing the UV-exposure operation in manufacturing thefluid-dynamic-pressure bearings, the oil repellant 33 was extremelyprone to peeling off, making necessary manufacturing operations todiscern the post-application peeling and reapply the repellant overagain. In contrast, the cohesiveness of the oil repellant 33 for sealsurfaces irradiated for 20 seconds with a UV beam having a principalwavelength of 185 nm was excellent, and thus in post-applicationinspections, there were almost no articles deemed to requirereapplication of the repellant. Consequently, reapplication work wasrendered practically unnecessary.

The diameter of the bearing housing 23 is about 10 mm, and the length ofthe mating fit between the bearing housing 23 and the mounting hole inthe bracket 27 is about 5 mm. Acryl-based anaerobic, UV-curing adhesiveagents, and epoxy-based thermosetting adhesive agents have each beenemployed to date as the adhesive 34. Prior to implementing theUV-exposure operation in manufacturing the fluid-dynamic-pressurebearings, the force required to pull the bearing housing 23 of adynamic-pressure bearing 2 out of the bracket 27 was 30-100 kgf. Incontrast, the force required to pull the bearing housing 23 of afluid-dynamic-pressure bearing 2 out of the bracket 27 when the gluingoperation is carried out under the same conditions, after the adhesionsurface of the housing has been irradiated for 20 seconds with a UV beamhaving a principal wavelength of 185 nm, is a dramatically improved60-120 kgf. Moreover, since the adhesive readily coheres to thecomponent surfaces, the adhesive spreads uniformly along the joiningfaces. Breaches between the adhesive and the components are consequentlynot liable to form, which thus makes it all the more possible to keepcontamination from the exterior from passing through such breaches andinvading the interior of a recording-disk drive.

Second Embodiment

Spindle motor 103, as illustrated in FIG. 3, is utilized as analternative to spindle motor 3 in the first embodiment. The recordingdisks 12 are carried on and spun by a rotor hub 121 of the spindle motor103.

The spindle motor 103 is, in a like manner as in the first embodiment,made up of a fluid-dynamic-pressure bearing 102, a stator 32, and arotor magnet 132. Likewise, in the spindle motor 103, a baseplate 127that constitutes a part of the case 11 for the recording-disk drive 1serves as the base component.

The fluid-dynamic-pressure bearing 102 includes: a columnar shaft 124mounted in the rotational center portion of the rotor hub 121; a sleeve122 having an inner circumferential surface that radially opposes theouter circumferential surface of the shaft 124; and the rotor hub 121,which has an underside surface that axially opposes the upper endface ofthe sleeve 122. The shaft 124 is composed of a hardened martensiticstainless steel, and the sleeve 122 is composed of a free-machiningstainless steel. A cylindrical wall member 126 encompassing the sleeve122 is attached to the rotor hub 121. The inner circumferential surface126 a of the cylindrical wall member 126 diametrically opposes the outercircumferential surface of the sleeve 122. The rotor hub 121, the shaft124, and the rotor magnet 132 constitute the rotor unit of the spindlemotor 103. Meanwhile, the sleeve 122, a stator 131, and the baseplate127 form the stator unit of the spindle motor 103.

At least a portion of the diametric gap between the outercircumferential surface of the shaft 124 and the inner circumferentialsurface of the sleeve 122 is rendered to measure some several .mu.m.Likewise, a portion of the axial gap between the upper endface of thesleeve 122 and the underside surface of the rotor hub 121 is rendered tomeasure several to 20.mu.m or so. Lubricating fluid 35 fills and isretained by these gaps: In the diametric gap, lubricating fluid 35 isretained, forming a radial dynamic-pressure bearing 142; and in theaxial gap, lubricating fluid 35 is retained, forming a thrustdynamic-pressure bearing 143. Furthermore, the inner circumferentialsurface 126 a of the cylindrical wall member 126 is a rotor-side sealsurface 145 a. Along the outer circumferential surface of the sleeve122, the portion that opposes the rotor-side seal surface 145 a is astator-side seal surface 145 b. The diametrical clearance between therotor-side seal surface 145 a and the stator-side seal surface 145 bflares going from the upper end to the lower end of the clearance. Thisclearance constitutes a capillary seal section 141. In the clearanceconstituting the capillary seal section 141, a boundary surface 144between the lubricating fluid 35 and the external atmosphere forms.

A method of manufacturing a fluid-dynamic-pressure bearing as set forthabove is as follows.

Namely, as is the case in the first embodiment, each component ismachined/formed, and then the components are cleaned.

Next, a plasma surface-treating process is implemented on the outercircumferential surface of the sleeve 122. In the present embodiment,ozone cleaning is utilized for the plasma surface-treating process.Ozone cleaning is carried out by ozonizing oxygen with an ultravioletbeam and exposing the outer circumferential surface of the sleeve 122with the resulting ozonic plasma. It will be appreciated that grease andother organic residues clinging to the component surfaces can be cleanedsimultaneously with the surface treating process.

Herein, the plasma surface-treating process may be implemented on theinner circumferential surface 126 a of the cylindrical wall member 126on the rotor hub 121, and on the vicinity of the mounting hole in thebaseplate 127.

Next, the shaft 124 is mounted into the rotor hub 121. Then the sleeve122 is fit over the shaft 124, and the cylindrical wall member 126 isattached to the underside face of the rotor hub 121. The cylindricalwall member 126 thus serves to lock the rotor hub 121 against coming outof the sleeve 122. The lower end (bottom) of the sleeve 122 is thencovered with an endplate 125. Thus the interior of the sleeve 122 ismade into a hermetic space.

Subsequently, along the outer circumferential side of the sleeve 122, inan area located to the lower side of the stator-side seal surface 145 b,oil repellant 33 is applied circuiting the circumference. The outercircumferential surface of the sleeve 122 onto which oil repellant 33 isapplied serves as a stator-side oil-repellant application surface 146 a.In turn, oil repellant 33 is also applied to the lower part of the innercircumferential surface 126 a of the cylindrical wall member 126. Theinner circumferential surface 126 a of the cylindrical wall member 126onto which oil repellant 33 is applied serves as a rotor-sideoil-repellant application surface 146 b. The bearing-manufacturingmethod then continues by heating the fluid-dynamic-pressure bearing 102to about 100° C. in order to cohere the oil repellant 33 to theoil-repellant application surfaces 146. Regarding the efficacy of theplasma surface-treating process, it is to be noted that there was nodiminishment of the resulting effectiveness even if the bearing washeated to as much as 120° C.

At this point lubricating fluid 35 is passed through the capillary sealsection 141 to charge the radial dynamic-pressure bearing 142 and thrustdynamic-pressure bearing 143 gaps with the fluid. Under a vacuumenvironment, with the sleeve 122 up and thus the rotor hub 121 down,lubricating fluid 35 is pooled in the capillary seal section 141opening. The volume of lubricating fluid is the amount according towhich the fluid-atmosphere boundary surface will form within the limitsdefined by the capillary seal section 141. After the bearing has beencharged with lubricating fluid 35, a check/inspection is made as towhether the boundary surface has formed in the correct position. Thebearing environment is thereafter repressurized gradually to atmosphericpressure, whereby the gaps are filled with the lubricating fluid 35.Therein, the lubricating fluid 35 is stably retained within the bearinggaps by capillary force acting in the gaps.

Next, the fluid dynamic-pressure bearing 102 is adhesively affixed intothe baseplate 127. A round mounting hole that closely matches the outercircumferential surface of the sleeve 122 is formed in the baseplate127. Adhesive 34 is applied to the inner circumferential surface of themounting hole, into which the sleeve 127 is then inset.

The stator 131 has in advance been mounted on the baseplate 127, whilethe rotor magnet 132 has in advance been attached to the rotor hub 121.In the foregoing way, the spindle motor 103 is completed.

It was confirmed that the effect on the wetting angle of the lubricatingfluid 35 in the capillary seal section 141 in the present embodiment wassubstantially equivalent to that when the bearing components wereUV-irradiated in the implementation in which an ultraviolet beam and thesame lubricating agent were utilized.

Similar effectiveness in making the oil repellant 35 less likely to peeloff was also confirmed. In particular, in the bearing having been heatedafter application of the oil repellant, the oil-repellant applicationsurface 146 b, which had been surface-treated with the plasma, wasscrubbed several dozen times at a force of 100 gf using a rag, yet nooil repellant was observed stuck to the rag. As will be understood fromthese confirmations, by applying the oil repellant 33 to the stator-sideoil-repellant application surface 146 a having undergone theplasma-based superficial treating process, the cohesiveness of the oilrepellant 33 is extraordinarily improved.

What is more, the adhesive strength between the baseplate 127 and thesleeve 122 is also improved, being at least more than twice the bindingstrength compared with the situation in which the surfaces are notplasma-treated. Consequently, the durability of the assembly againstshock or other impact improves dramatically.

Third Embodiment

The description now turns to FIG. 4, which is a diagram illustrating aspindle motor 203 and a fluid dynamic-pressure bearing 202 in yetanother embodiment of the present invention.

FIG. 4 is of a fluid dynamic-pressure bearing 202 in which the shaft 224is anchored into the bracket 227. This fluid dynamic-pressure bearing202 is made up of: a sleeve 222 mounted in a rotor hub 221 of thespindle motor 203; the shaft 224, which is inserted into the sleeve 222;and a flange 225 that is mounted on the upper-end part of the shaft 224.The gap between the sleeve 222 and the shaft 224 is charged with andretains lubricating fluid 35. A radial dynamic-pressure bearing 242 isformed in between the outer circumferential surface of the shaft 224 andthe inner circumferential surface of the sleeve 222. Furthermore, thrustdynamic-pressure bearings 243 a and 243 b are formed in between the topand bottom surfaces of the flange 225, and the sleeve 222 where itaxially opposes the top/bottom surfaces.

In this fluid dynamic-pressure bearing 202, the outer circumferentialsurface of the sleeve 222 and the lower endface of the sleeve 222 aresubjected to a plasma-based surface-treating process. It should beunderstood that these areas may also be inadiated with an ultravioletbeam. This surface-treating step may be either before or afterassembling the fluid dynamic-pressure bearing 202.

Oil repellant 33 is applied to the lower endface of the sleeve 222,after which the surface is heated to render a rotor-side oil-repellantapplication surface 246 a.

Next, lubricating fluid 35 is infused into the gaps by which the radialdynamic-pressure bearing 242 and the thrust dynamic-pressure bearings243 are formed. The lubricating-fluid 35 infusion method is the same asthat of the first embodiment.

The outer circumferential surface of the sleeve 222 is inset into amounting hole 227 a provided in the bracket 227, with adhesive 34intervening. A fluid dynamic-pressure bearing 202 of the thirdembodiment, owing to its retaining the lubricating fluid 35 stably, hasa long lifespan; wherein leakage of the lubricating fluid 35 in reactionto impact is restrained. In addition, in the spindle motor 203 also, theadhesive strength between the bracket 227 and the fluid dynamic-pressurebearing 202 is tough, which lends the motor an enhanced capacity towithstand impact.

It should be understood that the present invention is not limited onlyto the scope set forth in the embodiments, in that various modificationswithin a scope that does not depart from the gist of the presentinvention are possible. For example, substantially similar efficacy canbe achieved by carrying out whichever of the surface treatments-whetherit be a surface-treating process by ultraviolet-beam irradiation, or aplasma-based surface-treating process. Plasma-based surface-treatingprocesses comprehend various sorts of cleaning devices, such as thosefor ion cleaning, ozone cleaning, or UV-ozone cleaning, as well asirradiation by charged-particle beams and high-energy RF radiation.

Furthermore, of fluid dynamic-pressure bearings of the variousstructures that have been employed to date, the present invention isapplicable to fluid dynamic-pressure bearings furnished with a capillaryseal. Likewise, the present invention is applicable to spindle-motorimplementations in which the fluid dynamic-pressure bearing and othercomponents are joined by means of an adhesive, regardless of the form ofthe motor or the form of the bearing.

Other modifications include that the type of adhesive agent, the type ofoil repellant, the type of lubricating agent, and the materials andsubstances of the components that constitute the fluid dynamic-pressurebearing and the spindle motor may be varied according to use and design.Likewise, recording-disk drives of the present invention are notnecessarily limited to hard-disk drives; the present invention may beutilized in various sorts of recording-disk drives, such as removabledisk drives, optical disk drives, and magneto-optical disk drives. Stillfurther, a fluid dynamic-pressure bearing manufacturing method of thepresent invention may be utilized in implementations in which bearingsare manufactured for motors—such as motors for polygonal mirrors, andfan motors—that spin at high speed and in which a high degree ofrotational precision is mandatory.

1. A method in the manufacturing of a spindle motor which includes abase, and a stator unit received in the base with an outercircumferential surface of the stator unit facing an adhesion surface ofthe base, the method comprising: fabricating one of a component of thebase and a component of the stator unit of resin, a surface of thecomponent fabricated of resin constituting the outer circumferentialsurface of the stator unit or the adhesion surface of the base; treatingat least the surface of the component fabricated of resin with plasma orultraviolet radiation, wherein at least one of the outer circumferentialsurface of the stator unit and the adhesion surface of the base issurface-treated with plasma or ultraviolet radiation; applying adhesiveto at least one of the outer circumferential surface of the stator unitand the adhesion surface of the base; and subsequently sliding the outercircumferential surface of the stator unit along the adhesion surface ofthe base to thereby insert the stator unit into the base, and coheringthe stator unit and the base with the adhesive.
 2. A manufacturingmethod as set forth in claim 1, further comprising fabricating the otherof the component of the base and the component of the stator unit ofmetal, wherein a surface of the component fabricated of metalconstitutes the outer circumferential surface of the stator unit or theadhesion surface of the base; and cleaning the surface of the componentfabricated of metal with plasma or ultraviolet radiation before thestator unit is inserted into the base.